Clocks or other timing circuits are often used in electronic systems for enabling the operation of certain features or functions of the electronic systems. Electronic systems lose the time kept by a clock when power is shut off, and the clock will need to be reset. While some electronic systems may have a clock which displays a time, a clock in other electronic systems may be used to control an operation of the system. For example, a clock may be used to establish a warm-up period of time or may wait until mechanical components are stable. In the event of a power failure, the clock will be used to reset a warm-up period after power is resumed.
However, power shut-offs are often unintentional. For example, in the commercial domain, one-second power outages are common. These unintentional, short-term power outages often cause clocks to be reset. The power supply voltage may be unstable for a period of time. Mechanical devices such as motors or hard drives may still be moving while power is off to the electronics. When the power returns, the electronic system may not have any information regarding how long the power had been off. It must reestablish a clock which may be used in a start-up procedure. It must also consider attached devices for which different actions are necessary depending on how long they have been without power. For example, in certain electronic systems, the start-up period may be a warm-up period for a motor which requires time to reach operating speed or a lamp which needs to be heated to a certain temperature. However, without knowing how long the electronic system has been off, the electronic system will automatically restart the clock controlling the warm-up period, or may assume a motor is not turning when in fact it is still spinning, because power had been off only a very short time. Because the system may not have been off for long, restarting the warm-up period may lead to unnecessary delays in the operation of the electronic system. Resetting a motor speed to a small value if it is already moving rapidly may damage the motor or the attached components. It may also introduce electronic power surges. What is needed is an electronic device that can determine how long lower has been off, particularly for short power outages.